Synthesis and tautomeric structure of novel 3,7-bis(arylazo)-2,6-diphenyl-1H-imidazo-[1,2-b]pyrazoles in ground and excited states

Two series of novel 3,7-bis(arylazo)-2,6-diphenyl-1H-imidazo[1,2-b]pyrazoles were prepared starting from N-aryl 2-oxo-2-phenylethanehydrazonoyl bromides. The acid dissociation constants in both the ground and excited states, pK and pK∗, respectively, were determined for both series and were correlated by the Hammett equation. The results of such correlations together with spectral data indicated that the title compounds exist predominantly in the 1H-bis-(arylazo) form in both ground and excited states.